1. Field of the Invention
This invention relates to indicator systems comprising a container containing an environmental sensing system and compressible material separating the sensing system from its surroundings. Indicator systems can be used for the determination of sterilization in a variety of sterilizations processes or in determining the efficacy of an environmental test such as a test for air removal from a sterilization chamber.
2. Description of the Background
In health care, as well as many other industries, it is nearly always necessary to monitor the effectiveness of processes used to sterilize equipment such as medical devices, instruments and other disposable or nondisposable articles, and often waste. In these settings, sterilization is generally defined as the process of completely destroying all viable microorganisms including structures such as viruses, spores, yeasts and fungus. Standard practice in hospitals is to include a sterility indicator in a batch of articles to be sterilized. The use of sterility indicators allows a direct and sensitive approach to assay the lethality of the sterilization process.
A standard type of biological sterility indicator includes a known quantity of test microbial spores. This indicator is placed into the sterilization chamber and exposed to the sterilization process along with the objects to be sterilized. The test microorganisms, for example Bacillus stearothermophilus or B. subtilis spores, are incubated for a specified period of time under conditions which favor proliferation and examined for possible growth, such as turbidity in the growth medium or the presence or absence of certain metabolic products of any surviving microorganisms. Positive growth, indicating the presence of a viable spore, indicates that the sterilization process was insufficient to destroy all of the microorganisms. While the apparatus for containing the spores has varied continuously, the general sterility detection process has not. Many such indicators are disclosed in U.S. Pat. Nos. 3,239,429; 3,440,144; 4,596,773; 4,717,661; 4,732,850 and 5,167,923.
The largest use of sterility indicators occurs in research and the health care industry. Typically, such facilities have limited resources and must reuse their materials and instruments within 24 to 48 hours after sterilization and often immediately. Conventional sterility indicators normally require that the microorganisms be cultured for at least two and often up to seven days to assure adequate detection of any surviving microorganisms. During this time, items which go through the sterilization process, should not be used until the results of the spore viability test have been determined. Consequently, a holding period for sterility verification is often required. This holding period is both impractical and inefficient and, thus, the major drawback of all conventional sterility indicators.
The use of an enzyme and its subsequent activity as an indicator in detecting sterility has been described in U.S. Pat. No. 5,073,488. This technology has been greatly advanced with U.S. Pat. No. 5,486,459 which describes the use of a plurality of interactive enzymes. This technique involves subjecting a set of interactive enzymes to a sterilization cycle. Following completion of the cycle, the set is incubated with a substrate which is acted upon by the enzymes and transformed into a detectable product. Enzyme-modified product can be detected, for example, calorimetrically or fluorometrically. This method has been proven to be accurate and detection speeds are greatly accelerated as compared to spore systems. In fact, definitive results using interactive enzyme technology can be determined in less than a few minutes.
Sterility indicators are often placed in special packaging or wraps to simulate the condition of wrapped goods being processed in a sterilizer. If the articles to be sterilized are in special wrappings or packaging, the sterilant needs to effectively pass through the wrappings to destroy microorganisms on the article. To test the effectiveness of the sterilant passing through additional materials, sterility indicators are placed in challenge packs. These packs impede the sterilant as would the wrappings and thereby represent the conditions of wrapped goods in a sterilizer.
There are international standards such as the International Organization for Standardization (ISO) and the European Standards (EN) that deal with sterilization testing including steam sterilization. International standards dealing with biological indicators and testing procedures are found in the ISO 11138 series and EN 860 series. International standards for the air removal tests for pre-vacuum steam sterilizers comprises a chemical indicator in a test pack are found in the ISO 11140 series and EN 867 series. These packs incorporate the Bowie-Dick test and have similar performance standards as seen in AAMI (American Association of Medical Instrumentation), but use different testing procedures.
AAMI has proposed guidelines for challenge packs containing indicators that are assembled by hospital workers to simulate the conditions of wrapped goods in a steam or ethylene oxide sterilizer. Materials required for an AAMI challenge pack for a steam sterilizer include sixteen freshly laundered huck towels, autoclave tape and sterility indicators. In one method, each towel is folded length-wise into thirds and then folded width-wise in half. Towels are placed one on top of another with the folds opposite each other. Sterility indicators are placed between the eighth and ninth towels and the pack is secured with autoclave tape. The AAMI steam challenge pack is placed into a steam autoclave for the appropriate amount of time. Upon completion of a cycle, the indicators are processed to determine if the sterilization process was sufficient to inactivate the indicators buried in the pack.
In the case of ethylene oxide sterilization, AAMI recommends placing a sterility indicator into a plastic syringe so that the plunger is not touching the indicator. In this case, the needle end of the syringe is open. Two such syringes are placed in the center of a stack of folded towels and the stack is wrapped in a single towel. For routine monitoring, the syringe and indicator can be wrapped in a single towel and placed into a peel pouch.
Tests are also performed that evaluate the effectiveness of air removal in a prevacuum steam sterilizer. Prevacuum steam sterilizers are used to minimize the amount of air present in the sterilization chamber, thus enhancing the penetration of steam into porous loads. A prevacuum sterilizer air removal test is also known as the Bowie-Dick test or a prevacuum sterilizer residual air test.
AAMI guidelines for the Bowie-Dick test pack state that the standard pack is made using folded cotton surgical towels. Several towels are folded to create a stack 10 to 11 inches high with a rectangular border of 9 by 12 inches. A Bowie-Dick test sheet, which comprises a pattern of chemical indicator ink or indicator type on a porous sheet, is placed in the center of the pack. The pack is wrapped in a single cotton wrap and processed in a steam prevacuum sterilizer. The acceptance criterion is that the test sheet or tape darkens uniformly after processing. In other words, the chemical indicator ink changes color upon exposure to steam and if the entire sheet shows a uniform color change, there was no residual air to impede the steam.
AAMI guidelines state that other devices may be used in place of the AAMI challenge packs and Bowie-Dick tests if they provide equivalent results to the AAMI packs. Enclosure of sterilization indicators in various fibrous materials, analogous to textiles such as the towels used in the AAMI challenge packs, has been proposed in U.S. Pat. Nos. 5,200,147, 5,252,484 and 5,223,401. Packages in which a sterilization indicator is surrounded by porous material to replace some of the towels are described in U.S. Pat. No. 4,692,307.
Compressible material, such as foam, has a wide variety of uses when placed inside a container. For example, compressible material in a container could be used for absorbing shock vibrations or sound, as a barrier for solids, liquid or gases, for separating components, for absorbing liquids and/or for application of liquids such as ink, paint or antiseptics. A major drawback of using compressed material in a container is the expense of compressing the material into the container. The conventional process for inserting compressed material into a container was for the material to be compressed by hand and forced manually into the container. This method is slow, often unreproducible and, consequently, expensive.
U.S. Pat. No. 3,811,242 relates to an apparatus for compressing blocks of compressible material, particularly polyurethane, to a small percentage of their original volume by compressing in the direction of the longest axis of the block, successively, and in perpendicular directions until the block is of the desired size. Restraining bands are applied to the block to prevent rebound or expansion in all directions of compression.
U.S. Pat. No. 5,400,067 relates to an apparatus for inserting a rectangular foam insert into the rectangular ink chamber of an ink jet print head. The apparatus involves two flat pistons opposing two fixed plates which form a right angle. Pressure is exerted by each of the two pistons successively against two adjacent sides of the foam rectangle to compress the foam to a cross-sectional area smaller than the area inside the ink chamber. The ink chamber is positioned over a rectangular walled tube formed by extensions of the pistons and the opposing plates, and then a ram moving orthogonally to the two pistons pushes the foam into the ink chamber. This device requires successive compression in perpendicular directions by three moveable components.
U.K. Patent number 2,084,954 relates to a method for packaging a cylindrical sponge into a tube. The sponge is placed on a support plate between two jaws having concave arcuate section. According to this method, one jaw is fixed and a second jaw moves across the plate. Sponge is first compressed by a platen parallel to the support plate which descends toward the support plate until the separation between the platen and the support plate is equal to the desired diameter of the compressed sponge. Sponge is further compressed by movement of the moveable jaw across the plate until the two jaws abut, forming a cylindrical cavity containing the compressed sponge. The tube is axially aligned with the cavity and the sponge is pushed from the cavity into the tube by a plunger. This device requires successive compression in perpendicular directions by numerous moveable components that must be kept in perfect alignment.
U.S. Pat. No. 4,602,472 relates to a device for packaging rolls of fiber insulation by compressing them in a compression chamber which employs double stage compression. A pivoting stage compresses the roll in a first direction, analogous to the platen of U.K. Patent number 2,084,954. A ram having a concave semicylindrical surface compresses the roll in a second direction to form a cylinder of the desired size. Subsequently, a discharge ram pushes the roll along the axis of the cylinder into a tubular member suitably sized to receive the roll. A paper or plastic sleeve having a closed end is placed over the tubular member, and the roll pushed through the tubular member into the sleeve, thereby pulling the sleeve off the tubular member and enclosing the roll in the sleeve material.
U.S. Pat. No. 5,208,954 relates to a device for inserting, into cavities in masonry building blocks, preformed insulating foam inserts wherein the foam inserts are slightly larger than the cavities. In the device, the foam is positioned over a channel which in turn is aligned with the cavity in the block, the channel having a throat with curved sidewalls. A tamping head pushes the foam insert through the channel where the foam is compressed by the throat to have a cross-section small enough to fit into the cavity.
U.S. Pat. No. 3,450,036 relates to a device for packing loose granular material such as potting soil around a plant and depositing the packing material and plant into container, such as a pot or bag. The device includes at least two arcuate sections that fit together to form a cylinder holding the plant and soil. A ram pushes the plant and soil together out of the cylinder and into the container. As potting soil is not compressible to any significant degree, the device is a forming apparatus, but not a compressing apparatus.
None of these apparatus and methods are satisfactory for reproducibly inserting and positioning a compressible material such as foam or sponge into a vial.